1. Field of the Invention
This invention relates to an image forming apparatus such as a copier or a printer using the electrophotographic process, and particularly to the construction of an image forming unit detachably mountable to the image forming apparatus.
2. Description of the Related Art
An image forming apparatus using the electrophotographic process visualizes a latent image with a toner which is a developer, transfers the toner image to a sheet which is a recording material and fixes it to thereby form an image. In such an electrophotographic image forming apparatus, there is generally known a construction in which in order to form a color image in particular, toner images of a plurality of colors are superimposedly primary-transferred to an intermediate transfer member, and thereafter are collectively secondary-transferred to a sheet.
In a color image forming apparatus using an intermediate transfer member according to the conventional art, as shown, for example, in FIG. 10 of the accompanying drawings, an image bearing member unit 100 and an intermediate transfer member unit 101 are of independent cartridge construction. A large movable side frame 102 is provided on the front (the left side as viewed in FIG. 10) of the apparatus, and this is designed to be pivotally moved and opened to thereby mount or dismount the image bearing member unit 100 and the intermediate transfer member unit 101.
The image bearing member unit 100 is provided above the intermediate transfer member unit 101, and integrally has a photosensitive drum 103 and a waste toner collecting box 105. Waste toner on the photosensitive drum 103 is scraped off by a cleaning blade 104 and is collected into the waste toner collecting box 105 on the back thereof.
Waste toner on the intermediate transfer belt 106 of the intermediate transfer member unit 101 is also scraped off by a cleaning blade, not shown, and is carried to the lower portion of a first carrying pipe by a carrying coil, and is further carried to a portion above the waste toner collecting box 105 by a screw in the first carrying pipe. Thereafter, the waste toner is carried through the interior of a second carrying pipe by the carrying coil, and is finally collected into the waste toner collecting box 105. The connecting portion between the second carrying pipe and the waste toner collecting box is designed to be detachably attached as a discrete unit, and thus is designed such that the waste toner does not spill during the mounting and dismounting.
In the above-described construction, the image bearing member unit 100 and the intermediate transfer member unit 101 are independently positioned in the main body of the image forming apparatus, and the photosensitive drum 103 and the drive transmitting coupling of an intermediate transfer member belt 106 are also designed to be independently connected to the coupling of the main body side of the image forming apparatus.
Also, an example of the image forming apparatus according to the conventional art will now be described with reference to FIG. 11 of the accompanying drawings. The image forming apparatus shown in FIG. 11 is of a construction in which a photosensitive member belt 110, an intermediate transfer member belt 111 and a waste toner collecting box 112 are integral with one another. In the present construction, the photosensitive member belt 110 and the waste toner collecting box 112 are disposed in the downward projection direction of the intermediate transfer belt 111. Also, like the above-described first example of the conventional art, the image forming apparatus is of a construction in which a large movable side frame 113 is pivotally moved and opened to the front (the right side as viewed in FIG. 11) of the apparatus, and a unit comprising the photosensitive member belt 110, the intermediate transfer member belt 111 and the waste toner collecting box 112 made integral with one another is inserted from above.
Also, waste toner on the photosensitive member belt 110 and the intermediate transfer member belt 111, as in the above-described first example of the conventional art, is scraped off by respective cleaning belts, not shown, and is collected into the waste toner collecting box 112. However, the waste toner from the intermediate transfer member belt 111 is designed to fall downwardly by a carrying pipe, and is not a mechanism as complicated as the first example of the conventional art.
When the unit comprising the intermediate transfer member belt 111 and the photosensitive member belt 110 made integral with each other is positioned in the main body of the image forming apparatus, some positional deviation occurs on the unit side and the main body side of the apparatus as to the positional relation between the drive transmitting couplings of the photosensitive member belt 110 and the intermediate transfer member belt 111. So, in order to absorb the positional deviation, there is adopted so-called Oldham's coupling in which the intermediate member of the couplings slides on a claw portion and absorbs a misalignment.
However, in the construction as shown in the above-described first example of the conventional art wherein the image bearing member unit 100 and the intermediate transfer member unit 101 are provided discretely from each other, the drive transmitting couplings are positioned independently of each other and therefore misalignment does not occur, but yet there is the problem that the entire apparatus becomes bulky. Also, the opening portion for the mounting and dismounting of the units becomes large and complicated, and this leads to an increase in cost. Further, the presence of two kinds of process cartridges may cause a predetermined mounting and dismounting procedure, and this may lower the operability to a user.
Also, in the second example of the conventional art, the photosensitive member belt 110 and the intermediate transfer member belt 111 are an integral unit, and the so-called Oldham's coupling is adopted to absorb the misalignment of the respective drive transmitting couplings. Further, the drive transmitting coupling of the main body side of the apparatus is designed to axially slide and retract in operative association with the operation of opening and closing a door to mount or dismount the units, and the construction of the coupling is very complicated. Also, to sufficiently bring out the performance as the Oldham's coupling, a coupling of good accuracy is necessary. By these reasons, the above-described drive transmitting couplings are very high in cost and require a very large space.